It’s kind of a double edged sword. On the one hand, by using a sub, you can take the most demanding frequencies off your larger driver (8 inch in your case), relegate it to upper bass and mids, and lower distortion in those lowest frequencies some (like why a lot of studio engineers swear by 3-way designs as opposed to 2-way). And, by being able to position your sub freely, you can minimize the impact it has on the sound at the listening position by moving the modes around the room.
OTOH, adding a sub means adding a crossover filter, and that means you need to worry about phase issues at the crossover point. And the crossover has to be usually between 80 and 250 hz, where there’s a lot of important things happening, so you need to get that crossover really, really right. In normal multi-driver speakers, this is taken care of by the manufacturer, but when adding a sub to system after the fact, it’s on you unless they’ve specifically developed the speakers and sub with each other in mind.